It has been shown that the microsuspension, or fine suspension, process for producing homopolymers or copolymers of vinyl chloride, results in several operational advantages, in particular, control of particle size and decreased incrustation of reactor surfaces. Polymerization in microsuspension is understood to involve three main steps:
(1) The dispersion step wherein the water and the monomer or monomers required for the seed polymerization step are vigorously agitated in the presence of the amount of an organo-soluble initiator required for both the seed polymerization step and the microsuspension polymerization step in order to form an aqueous dispersion of particles having an average diameter of less than 5 microns;
(2) the seed polymerization step wherein the temperature of the dispersion from the prior step is raised, under autogenous pressure, until polymerization begins, then controlled until the seed polymerization is completed; and
(3) the microsuspension polymerization step wherein the seeding product of the seed polymerization step, containing all the initiator for the microsuspension polymerization, is added to the monomer or monomers in an aqueous medium, followed by raising the temperature of the mixture until the polymerization begins, then controlling the temperature until polymerization is complete.
Since all the initiator necessary for the microsuspension polymerization of the monomer is present in the considerably smaller seed polymerization batch, it poses the potentiality for the rapid decomposition of the initiator with possible adverse effects to the seeding product as well as to the equipment in which it is produced. To protect against such a potentiality, inhibitors have been used in the seed polymerization step to chemically react with the decomposition products of the initiator and thus limit the number of free radicals present. Heretofore, the inhibitors used, while effective in controlling initiator decomposition, have suffered the disadvantages of being irritants affecting operating personnel and of imparting objectionable color to the polymerized product and other products made therefrom.